1. Field of the Invention
The present invention relates to a method for programming a memory structure, and more particularly, to a method for programming a memory cell by injecting an electron or a hole generated by gate-induced drain leakage (GIDL) or band-to-band tunneling (BTBT) effects at adjacent memory cells.
2. Description of the Prior Art
A semiconductor memory can be divided into two categories: dynamic random access memory (DRAM) and non-volatile memory. The difference between these categories is whether the stored data can be reserved for a long time when external electric power is turned off. The data stored in the DRAM will disappear but the data stored in the non-volatile memory will be preserved. Currently, flash memory is a mainstream non-volatile memory, which can be further divided into NOR flash and NAND flash. The NAND flash has the advantages of high capacity, faster programming speed, and smaller device area.
When performing programming operations, the flash memory disposes electrons in a floating gate. When performing erasing operations, the flash memory moves the electrons from the floating gate. At present, there are two major methods of disposing the elections in the floating gate. In the first method, the electrons inside the channels are sped up by a depletion region for obtaining enough energy to stride across an oxide layer energy barrier by injecting channel hot carriers, thus the electrons are injected into the floating gate. In the second method, a voltage for generating the Fowler-Nordheim tunneling effect is added between the control gate and the substrate, thus the electrons are moved from the substrate to the floating gate through the oxide layer. These two methods respectively have their advantages and disadvantages. By adopting the method of injecting the channel hot carriers, elements need not operate under a very high voltage but a larger power consumption is needed when programming data. On the other hand, by adopting the method of injecting electrons through the tunneling effect, a lower power consumption is needed but a sufficient electronic field is necessary for the oxide layer to induce the tunneling effect on the electrons. Therefore, high voltage operations cannot be avoided, which are usually between 20V-30V. Hence, how to improve efficiency for erasing/programming a memory, how to lower operation voltage and power consumption, and how to improve disturbance immunity are important topics to be considered when designing a memory.